Risk Evaluation Triangle (RET) For Landslide Risk Management (LRM): A Case Study from Kota Kinabalu, Sabah, Malaysia

Landslide Risk Evaluation (LREv) is a decision-making process for Landslide Risk Analysis (LRAn) results. This process determines whether the inherent risks are acceptable, tolerant, unacceptable or a detailed studies is required. LREv also involves consideration of risk perceptions, risk communication and risk comparisons aimed at developing appropriate steps or level of response. Part of the LREv procedure is to assess the risk acceptance criteria. To achieve this goal, the F-N curve is used. The F-N curve relates to an annual probability that may cause n or more fatalities (F) to the total fatalities (N). The F-N curve is a complementary cumulative distribution function and provides statistical observations for all levels in offsetting a risk. However, the results of the LREv study on the previous F-N curves indicate that there is a constraint in the context of continuity of the proposed method or extension for the appropriate Landslide Risk Management (LRM) approach. Therefore, to overcome this shortcoming, a diagram known as the "Risk Evaluation Triangle (RET)" was introduced. RET basically aims to assess the level of Risk Tolerance Index (RTI) quantitatively. The parameters involved are Landslide Hazard Analysis (LHAn) and fatalities estimation. RTI levels are classified from very low ( 0.81) and follow-up detailed description are given. Hence, these RET outcomes are expected to serve as a continuation of the advanced method or approach in uniform LREv which has a coordination principle that can be developed for LRM purposes

CORRELATION OF MICROSTRUCTURE CHARACTERISTICS WITH THE SLOPE STABILITY AT TRUSMADI FORMATION, SABAH, MALAYSIA

This study focuses on the influence of weathered rock’s microstructure and its effect to the stability of slope at the Trusmadi Formation. Trusmadi Formation (Palaeocene to Eocene age) had experience a slightly metamorphism process and makes it highly susceptible to instability. Regional metamorphism that happened during tertiary has given rise to the formation of argillaceous rock. This rock then suffering a weathering process that change them to soil. Four samples were collected based on fail slope and stable slope. These samples were analysed using polarizing microscopic and scanning electron microscopic (SEM). Microstructural features identified that all slopes had the same platy minerals and mineral grain size and shape except for the cracks and porosity percentage. Percentage of cracks and porosity in stable slope are 35% and 40% in the average while 55% and 65% in fail slope. For SEM study, the percentage of porosity is 37% for stable slope and 55% for fail slope. The presence of 1:1 clay that is kaolinite gives only a small impact to slope stability

Geohazards In Sandakan Town Area, Sabah, Malaysia.

The geology of the Sandakan town area provides a favourable setting for geomorphological hazards occurrences. The exposed rocks in the study area and its surrounding vary in types and ages, from Late Eocene-Early Miocene Neogene’s clastic sediment of the Garinono Formation, the Sandakan Formation and Volcanic Facies to vary recent Quaternary alluvial materials which are still being deposited. These rock units are dissected by numerous lineaments with complex structural styles developed during series of regional Tertiary tectonic activities. Rapid urbanization activities have caused changes in the land use. Urbanization processes may contribute to the exposure of impervious surface, loss of vegetation cover, modification of slope gradient and drainage systems. The last decade has seen slope failure, flash flood and erosion events, which have claimed lives, damaged properties and increased the cost of maintenance. The main factors causing geomorphological hazards occurrences in the study area are natural (geology, meteorology, topography and drainage system) and human factors (lack of proper planning, human activities and community’s attitude). Serious efforts to increase the community’s awareness to geomorphological hazards occurrences and reconstruction of natural ecosystem must be taken. To handle this issue, both prevention and mitigation are necessary. At the planning level a multi disciplinary approach to zoning, risk assessment and design with construction practices is recommended. This is to ensure that future activities will not cause further damage to natural environmental condition or ecosystem

Landslide Density Based on Time Series

Abstract—Landslide density analysis based on a temporal landslide distribution over three different years was conducted in Kundasang, Sabah, Malaysia. The analysis involved landslides that occurred in 1984, 2009 and 2012. The objective of this study is to examine the relationship between the physical parameter and landslide density analysis based on temporal landslide distribution. This is the preliminary study for landslide hazard assessment. Landslides in these three assessment years were identified based on aerial photographs interpretation. The landslides detail has to be digitised as points and the point density was calculated using 1 km x 1 km grid on the landslide inventory map. From the analysis, there were 494 landslides distributed across the assessment years and by using the natural break classification, the landslide density map was classified into three classes of density, resulting low (1 landslide), moderate (2-3 landslides) and high (>4 landslides). Based on the landslide density analysis, there are 48 km2 that were identified as highly susceptible to landslide. Out of the high landslide density area, 46km2 were indicated as the most susceptible location for landslides due to the type of lithology that may lead to land sliding. This study indicates that the lithology played an important role as they can influence the geomorphologic process, and can induce landslides. As a conclusion, this study found that using the grid technique is an effective way to determine landslide density and detail investigation should be conducted to minimize the impact of landslide occurrences before any development could take place.&nbsp

Engineering Geological Mapping On Slope Design In The Mountainous Area Of Sabah Western, Malaysia.

The geology in the mountainous area of Sabah western provides a favourable setting for engineering geological instability. The area is underlain by the Trusmadi Formation (Palaeocene to Eocene age), the Crocker Formation (Late Eocene to Early Miocene age) and vary recent Quaternary alluvial materials which are still being deposited. The argillaceous nature and intense deformation suffered by the Trusmadi Formation and the highly jointed sandstone and mudstone beds of the arenaceous Crocker Formation makes them highly susceptible to weathering and instability. The weathered materials are unstable and may experience sliding due to by high pore pressure and intensively of geomorphological processes. In this study, a total of 20 selected critical slope failures were studied and classified into two main groups; rock slope (ten) and soil slope (ten). Soil slope failures normally involved large volumes of failed material as compared much rock slopes, where the failures are mostly small to medium. Kinematics rock slope analyses indicates that the variable potential of circular, planar, wedges, and toppling failures modes as well as the combination of more than one mode of aforementioned failure. Rock and soil slopes stability analysis indicates that the factor of safety value as unsafe (0.56 to 0.95). The geological influence had transformed the slopes in the Sabah mountainous area to be highly unstable and susceptible to landslide occurrences. Six (6) related main parameters to the landslide occurrence in the study area were attributed; 1) local and regional geology, 2) hydrological and geohydrological, 3) mineralogical and micro structures, 4) local discontinuities structures, 5) physical and engineering properties of soil and rock, and 6) geomorphological processes which can help in evaluating landslide problems. Therefore, development planning has to consider the slope hazard and risk management. This engineering geological mapping may play a vital role in disaster risk reduction programme in Sabah to ensure the public safety and to be extend with different environment

Flood Susceptibility Analysis using Multi-Criteria Evaluation Model: A Case Study in Kota Kinabalu, Sabah

This study focused on the Flood Susceptibility Analysis (FSA) of the Kota Kinabalu area, Sabah by using Multi Criteria Evaluation Model (MCE). The study area had been affected by flood throughout the years. The aims of this study are to determine the flood susceptibility level of the study area and to identify the contributing factors that leads to the flood disaster. Thus, a few mitigation measures can be recommended. The contibuting factors that leads to flood disaster had been identified through desk studies and fieldwork. The data were obtained and digitized using ArcGIS software and the thematic maps were produced. The factors that contributing to flood disaster such as slope gradient, elevation, topographic curvature, flow accumulation and drainage distance were retrieved from the topographic database, whereas the land use, rainfall and soil types from various agencies. Several areas are considered as susceptible, such as areas of Taman Kingfisher, Kg. Bantayan, Menggatal area, and Kg. Tebobon. To avoid or minimize the flood disasters, the Flood Susceptibility Level Map can be used in future development planning and a few structural control can be implemented such as the reconstruction of drainage in the study area and a warning system. This study can be used as a resource for consulting, planning agencies and local governments in managing risk, land-use zoning and remediation efforts to mitigate risks

Peta ketumpatan fizikal bagi menentukan unsur berisiko banjir di kawasan Kota Belud, Sabah, Malaysia

Banjir merupakan bencana alam yang berlaku setiap tahun dan memberi impak kepada kehidupan manusia, gangguan sosio-ekonomi dan kemusnahan alam sekitar. Terdapat tiga komponen penting dalam mentafsir risiko banjir iaitu; Bahaya, Kemudahterancaman dan Pendedahan. Pendedahan dalam konteks ini merujuk kepada unsur yang terdedah atau berisiko kepada sesuatu kerugian dan mempunyai tahap kemudahterancamannya yang tersendiri. Rekod kejadian banjir di kawasan ini semakin meningkat terutamanya selepas kejadian Gempa Bumi Ranau 2015. Peningkatan kejadian ini menjejaskan kelangsungan hidup kerana kebergantungan komuniti setempat terhadap hasil pertanian seperti penanaman padi untuk menjana pendapatan selain penempatan kemudahan fasiliti awam seperti hospital, pejabat kerajaan dan sekolah. Justeru, mengenal pasti unsur berisiko di kawasan ini amatlah penting untuk meminimumkan risiko banjir yang akan menjejaskan kawasan ini. Objektif utama kajian ini adalah untuk mengenal pasti unsur berisiko yang terdedah kepada ancaman bencana banjir di kawasan Kota Belud, Sabah. Pendedahan unsur berisiko boleh dikenal pasti secara nyata atau tidak nyata. Unsur berisiko nyata dikenal pasti melalui jejak bangunan dan jenis jaringan jalan raya yang ada di sekitar kawasan kajian manakala unsur berisiko tidak nyata pula, analisis ini dilakukan secara soal selidik di lapangan. Peta Ketumpatan Fizikal (PKF) kemudian dihasilkan daripada jejak bangunan dan peta jaringan jalan raya untuk menggambarkan unsur berisiko pada skala rantau. Peta ini dihasilkan dengan menukar poligon bangunan menjadi titik dan pengiraan dibuat berdasarkan kilometer persegi dan menggabungkannya dengan maklumat ketumpatan jaringan jalan raya. Kaedah ini turut digunakan sebagai kaedah alternatif untuk menggambarkan taburan penduduk bagi kawasan yang mempunyai ketersediaan dan kebolehcapaian data yang terhad. Hasil analisis menunjukkan kawasan unsur berisiko yang berketumpatan fizikal tinggi terletak berhampiran dengan sungai-sungai utama seperti Sungai Kadamaian, Sungai Wariu, Sungai Gurong-gurong, Sungai Tempasuk dan Sungai Abai. Kajian ini amat berguna sebagai kajian perintis dalam mentafsir risiko banjir di kawasan ini dan berpotensi dikembangkan di kawasan lain agar kerosakan dan kerugian harta benda, infrastruktur atau utiliti awam dapat diurus dan dikurangkan

Analisis indeks kemudahterancaman banjir secara fizikal, sosial dan persekitaran di kawasan Kota Belud, Sabah, Malaysia

Banjir merupakan bahaya semula jadi yang boleh mengancam nyawa dan harta benda. Salah satu aspek penting dalam pentaksiran risiko banjir adalah kemudahterancaman. Kemudahterancaman ditakrifkan sebagai keupayaan sesuatu unsur berisiko untuk terancam akibat suatu fenomena berbahaya. Peningkatan kejadian banjir di kawasan ini semakin kerap terutamanya selepas kejadian Gempa Bumi Ranau 2015. Pemindahan penduduk mungkin satu faktor utama dalam menyelesaikan masalah banjir, namun hakikatnya penduduk enggan untuk berpindah dan bersedia untuk berhadapan dengan risiko bencana banjir. Justeru, memahami darjah kemudahterancaman unsur berisiko di kawasan ini amatlah penting untuk meminimumkan risiko banjir di kawasan ini. Objektif utama kajian ini adalah untuk mentaksir kemudahterancaman banjir di kawasan Kota Belud berdasarkan tiga parameter utama iaitu secara fizikal, sosial dan persekitaran. Kajian ini mengambil kira unsur berisiko yang terdedah kepada kemudahterancaman banjir seperti bangunan dan komuniti setempat. Kajian ini dijalankan secara rantau bagi menggambarkan keadaan keseluruhan kawasan kajian sebelum, semasa dan selepas kejadian banjir berlaku. Sebuah pangkalan data dihasilkan dengan mengambil kira integrasi antara parameter kemudahterancaman dan pengenalpastian unsur berisiko. Data ini kemudiannya dicerap di lapangan untuk pemberian nilai skala bagi setiap parameter kemudahterancaman seperti berikut: skala 0 (tiada kerosakan), 0.25 (kerosakan rendah), 0.5 (kerosakan sederhana), 0.75 (kerosakan tinggi) dan 1 (kerosakan total). Penetapan nilai skala ini dibuat untuk memastikan keseragaman dalam menilai sub-parameter kemudahterancaman banjir di kawasan kajian. Selepas pengiraan skala kemudahterancaman dibuat, peta hasil pengiraan parameter kemudahterancaman dijana menggunakan teknik interpolasi bertujuan untuk menentukan nilai kebarangkalian bagi lokasi yang mungkin tidak dapat dikenal pasti atau tidak mempunyai data. Ketiga-tiga parameter kemudahterancaman kemudiannya digabungkan menjadi peta kemudahterancaman banjir di kawasan ini. Hasil pengiraan skor kemudahterancaman keseluruhan ini, sebanyak 533 (3.51%) buah bangunan yang terdapat di kawasan kajian mempunyai nilai 0.00 - 0.20 iaitu dalam kategori sangat rendah, 3,092 (20.37%) buah bangunan mempunyai nilai 0.21 - 0.40 iaitu dalam kategori rendah, 9,561 (62.98%) buah bangunan mempunyai nilai 0.41 - 0.60 iaitu dalam kategori sederhana, 1,995 (13.14%) buah bangunan mempunyai nilai 0.61 - 0.80 iaitu dalam kategori tinggi dan tiada jumlah bangunan mempunyai nilai 0.81 - 1.00 iaitu dalam kategori sangat tinggi. Hal ini mungkin dikaitkan dengan sub-parameter kemudahterancaman sosial kerana tiada kecederaan atau kematian direkodkan sepanjang kejadian banjir yang berlaku di kawasan kajian terutamanya selepas kejadian Gempa Bumi Ranau 2015. Tahap kesedaran awam atau kesiapsiagaan penduduk dalam menghadapi banjir juga dilihat tinggi. Ini menunjukkan bahawa penduduk setempat sudah boleh mengadaptasikan diri mereka dengan keadaan banjir yang sering berlaku di kawasan ini sejak tahun 1960-an lagi. Namun begitu, tahap kemudahterancaman yang berada pada kelas tinggi harus diberi perhatian kerana ia boleh memberi kesan secara langsung kepada aktiviti sosio-ekonomi

Engineering Geological Study On The Slope Failure Along The Kimanis To Keningau Highway, Sabah, Malaysia.

The geology along the Kimanis to Keningau Highway provides a favourable setting for engineering geological instability. The area is underlain by the Crocker Formation (Late Eocene to Early Miocene age) to vary recent Quaternary alluvial materials which are still being deposited. Crocker Formation consists mostly of interbedded grey sandstones and grey mudstones or shales. The sandstones are texturally immature where angular to subrounded quarts grains are cemented by clay minerals and occasionally by calcite. The Crocker Formation has also undergone intense deformation. The tectonic complexities influenced the physical and mechanical properties of the rocks, resulting in a high degree of weathering and instability. The weathered materials are unstable and may experience sliding due to by high pore pressure and intensively geomorphological processes. In this study, a total of 28 selected critical slope failures were studied and classified into two main groups: rock slope and soil slope. Failures in soil slopes (including embankments) are 18 (64 %) whereas 10 of all failures (36 %) of rock slope. Soil slope failures normally involved large volumes of failed material as compared much rock slopes, where the failures are mostly small. Of the 18 failures in soil slopes, 6 (33 %) are embankment failures making them 21 % of all types of failures. Kinematics rock slope analyses indicates that the variable potential of circular, planar, wedges and toppling failures modes as well as the combination of more than one mode of aforementioned failure. Rock and soil slopes stability analysis indicates that the factor of safety value as unsafe (0.50 to 0.96). The main factors causing slope failure occurrences in the study area are natural (geology, meteorology, topography and drainage system) and human factors (lack of proper planning, human activities and community’s attitude). Development planning has to consider the hazard and environmental management program. This engineering geological study should be prioritized and take into consideration in the initial step in all infrastructures program and it may play a vital role in landslide hazard and risk assessment to ensure the public safety

Flood susceptibility assessment (FSA) using GIS-based frequency ratio (FR) model in Kota Belud, Sabah, Malaysia

The flood is one of the most devastating natural disasters to strike Sabah, Malaysia, especially in the Kota Belud region. The Flood Susceptibility Analysis (FSA) was described using bivariate statistical analysis (the Frequency Ratio model) based on a Geographical Information System (GIS). Field surveys and formal reports from local authorities in the study area created the flood inventory map. The training dataset for statistical analysis consisted of 100 flood locations inundated in 2017, while the validation dataset consisted of 54 flood locations from the 2016 flood report. Eight (8) parameters (elevation, slope curvature, slope angle, topography wetness index, drainage density, drainage proximity, land use, and soil type) were extracted from the database and then converted into a raster format with a cell size of 5m x 5m. Finally, using the natural break classification method, the FSA was generated and classified into five classes: very low, low, moderate, high, and very high susceptibility. The area under the curve (AUC) analysis validated the flood susceptibility model's accuracy. The success rate AUC was calculated to be 0.89, while the prediction rate AUC was 0.82. The flood susceptibility analysis could be used to develop flood mitigation strategies in land use planning